The present invention concerns an inter-shaft bearing for multibody turbojet engines comprising a device for the damping of vibrations by means of a film of oil.
Multibody turbojet engines contain a bearing which supports a first shaft in relation to a second shaft and which comprises in a general manner a roller bearing inserted between an inner bushing mounted on the first shaft and an outer bearing contained in a box, which in turn is mounted on the second shaft. The bearing also contains a lock nut maintaining the inner bushing on the shaft. In a more precise definition, the first shaft consists of the line journal of the shaft of the high pressure body and the second shaft consists of the line journal of the shaft of the low pressure body. At the present time, in order to obtain a satisfactory operation of a bearing of this type, two functions must be performed: on the one hand, the lubrication and cooling of the roller bearing, and on the other, the damping of vibrations normal to the shafts and the roller bearing, must be assured.
French Pat. No. 2,208,050, filed on Nov. 23, 1973, provides an illustration of the solutions applied in the case of a bearing supporting a shaft rotating in relation to a stationary structure, in order to satisfy these operating requirements. Thus, as described by the patent, the lock nut comprises on its internal face and annular groove supplied with oil, which is then distributed over the inner bushing to ensure the lubrication and the cooling of the rollers. After leaving the bearing, the oil arrives on the outer bushing, in a space provided between the outer bushing and the roller box, where the film of oil formed under pressure, acts to damp the vibrations.
Another French Pat. No. 1,384,980, filed on Jan. 8, 1964, envisions the case of an inter-shaft bearing, for which, from a common inlet, oil is distributed on the one hand, over the ball bearing for lubrication, and on the other through an annular chamber toward a plurality of recesses provided in the outer bushing, for cooling. The entirety of the oil is then returned, through a common return conduit, for recycling.
However, these solutions of the prior art are not entirely satisfactory. The interdependence, for example, of the supply under pressure of the damping film of oil and the lubricating conduit of the bearing does not allow the adjustment of the necessary flow rates for each function and makes it difficult to obtain constant damping depending on a predetermined flow rate and pressure of the oil supplying the film formed between the outer bushing and the box of the roller bearing. It should be noted that the quality of the results obtained is particularly important for an application to multibody turbojet engines in view of the high velocities demanded and the severe conditions of utilization.